The present invention relates generally to external defibrillators. In particular, the invention relates to automatic external defibrillators that can be continuously and easily worn by a patient for an extended period of time.
Every year in the US, over 800,000 individuals have a heart attack, or myocardial infarction (MI). After an MI, a patient is at increased risk for experiencing potentially life-threatening abnormal heart rhythms, or arrhythmias. This increased risk is caused by numerous structural and electrical abnormalities in the recently damaged heart. For most patients, however, this increased risk is temporary. After patients have been treated with various procedures and medications to help their heart heal, their risk of experiencing a life-threatening arrhythmia usually drops back to their risk prior to the MI. This drop in risk typically occurs after a few days to weeks after the MI has taken place.
Various studies of this population of patients have shown that certain medications, especially those with anti-arrhythmic properties, do a poor job at reducing this temporarily increased arrhythmia risk. Additionally, implantable cardioverter defibrillators (ICDs), which are devices that can effectively reset the heart rhythm when an arrhythmia occurs, carry significant risks during implantation such that their overall benefit during this short period of increased risk is limited. Implanting ICDs in many patients whose risk of an arrhythmia would eventually return to normal also has significant unwanted health, economic, and societal consequences.
Automatic external defibrillators (AEDs), which can be very effective in highly populated places such as airports, are only useful if other people capable of using the AED are present at the time an arrhythmia occurs and can identify that a patient needs defibrillation; this may often not be the case for most people living at home. Finally, current methods of temporary defibrillation, such as wearable defibrillator vests, are not routinely used due to difficulty for patients to comply with such systems because of the obtrusiveness of the device, the inability to use such systems when wet, etc. Wearable external defibrillators and external cardioverter defibrillators are described in U.S. Pat. Nos. 5,741,306; 6,065,154; 6,280,461; 6,681,003 and US 2003/0095648, and a similar product is currently being sold as the Zoll Lifecor LifeVest™ wearable cardioverter defibrillator. Due to all of these limitations, the vast majority of patients are sent home after an MI without any type of temporary protection from a potentially life-threatening arrhythmia.
In addition to the post-MI setting, there are other situations in which a patient's arrhythmia risk is temporarily increased, such as after certain types of heart surgery or when starting certain medications with pro-arrhythmic properties. In patients who are known to be at risk for an arrhythmia and who have an ICD in place, if the ICD needs to be removed for a short period of time due to an infection or malfunction, the patient is also left vulnerable. In other patients, such as those with a condition known as heart failure, certain medications and/or procedures can lead to an improvement in the heart's function and reduce a patient's susceptibility to an arrhythmia such that a permanently implanted device, such as an ICD, would not be needed. However, during the time of treatment when heart function is recovering, these patients are still temporarily at risk for a life-threatening arrhythmia.